1. Field of the Invention
This invention relates to an ink composition, and more particularly, to an ink composition suitable for ink jet printing.
2. Description of Related Art
Many types of printing inks have been developed for satisfying a variety of purposes. For some applications, it is desirable to provide an ink which provides superior printing qualities. Generally, these inks have a high surface tension and are relatively slow drying. For other applications, it is desirable to provide an ink which is fast drying. These inks typically have a lower surface tension than the slow drying inks, and tend to wick unevenly (feather) when printed on paper, resulting in poor print quality.
In some applications of printing with inks, the drying time of images is a significant characteristic to consider. In particular, in printing processes such as ink jet printing, the drying of the ink can be particularly critical. For example, it may be desirable to provide fast drying inks for increasing throughput. However, fast drying inks typically provide poor print quality because of feathering. Further, inks may clog the nozzles of the ink jet because of the speed at which water evaporates from the nozzles.
Slow drying inks, while providing good print quality, put constraints on the design and the speed of ink jet printers. Therefore, there is a need for ink formulations which are fast drying while still maintaining good print quality. Good print quality is usually achievable with inks that have a high surface tension (greater than 50 dynes/cm) and are slow drying (greater than 20 seconds on most plain papers).
In addition to providing good print quality, it is also desirable that an ink have good jetting characteristics without deterioration of the ink jet nozzles. The deterioration of the ink jet nozzles may be described in terms of the ink's latency. Latency, as used herein, refers to the maximum time period, usually less than an hour and most often less than 10 minutes, over which an uncapped ink-jet printhead can remain idle before noticeable deterioration of its jetting performance.
U.S. Pat. No. 4,530,961 to Nguyen et al. discloses a low viscosity stable aqueous dispersion of graft carbon black for manufacturing ink compositions. An aqueous dispersion of carbon black is grafted with hydrophilic monomers such as alkali or ammonium carboxylate bearing polymers. In preparing the grafted carbon black, a peroxidation step is performed which may be carried out in the presence of a free radical polymerization accelerator such as an amine accelerator. One of the disclosed accelerators is TRIS-TEMED, tris-(hydroxymethyl)-aminomethane-N-tetraethylethylene diamine.
U.S. Pat. No. 4,154,618 to Burke discloses coating compositions useful for inks which provide films which are water-resistant and which have excellent wet/dry rub resistance. The coating compositions comprise acidic resins, a metal-polyamine complexer, and optional organic acids and cometals. The acidic resins may be derived from amine or blocked amine alcohols such as tris(hydroxymethyl)aminomethane and triethanolamine.
While many types of inks are available, it is desirable to provide improved ink compositions which are fast drying while also maintaining good print quality.